Non-woven mats by melt blowing

ABSTRACT

Melt blown non-woven mats prepared from thermoplastic polymer fibers and substantially completely free of polymer shot are produced at high polymer throughput rates in an improved melt blowing process in which thermoplastic polymer resins, preferably polypropylene, having initial intrinsic viscosities of at least 1.4, are degraded, optionally in the presence of a free radical source compound, to have both reduced intrinsic viscosities and an apparent viscosity in the melt-blowing nozzle orifices of from about 50 to about 300 poise.

United States Patent [191 Butin et al.

[451- Nov. 19, 1974 NON-WOVEN MATS BY MELT BLOWING [75] Inventors:Robert R. Butin; James P. Keller; John W. Harding, all of Baytown, Tex.

[73] Assignee: Exxon Research and Engineering Company [22] Filed: Feb.22, 1972 [21] App]. No.: 227,769

Related U.S. Application Data [63] Continuation-impart of Ser. Nos.865,105, Oct. 9, 1969, Pat. No. 3,755,527, and Ser. No. 103,050, Dec.31, 1970, abandoned, and Ser. No. 103,094, Dec. 31, 1970, abandoned,said Ser. No. 103,050, and Ser. No. 103,094, each is acontinuation-in-part of Ser. No. 786,122, Dec. 23, 1968, abandoned.

[52] U.S. Cl. 161/169, 156/167, 264/176 F, 264/210 F, 264/211 [51] Int.Cl. F06b 9/30 [58] Field of Search 264/210 F, 176 F, 121; 156/167, 181,62.4, 229, 244; 161/169, 402; 425/71 [56] References Cited UNITED STATESPATENTS 3,013,003 12/1961 Maragliano et al 260/93.7 3,143,584 8/1964Roberts et al. 264/210 F 3,502,763 3/1970 I-lartmann 3,543,332 12/1970Wagner et al. 264/176 F DIE HEAD /BLOWN FIBERS 7 ,w.

3,551,943 1/1971 Staton et al l8/2 3,595,245 7/1971 Buntin et a1.131/269 3,615,995 10/1971 Buntin et al.. 156/161 3,615,998 10/1971 Kolbet a1. 156/167 3,634,573 l/1972 Wagner et al.... 264/210 F 3,676,2427/1972 Prentice... 156/297 3,755,527 8/1973 Keller et al 264/176 F OTHERPUBLICATIONS Superfine thermoplastic Fibers, by Wente, Ind. Eng. Chem,Vol. 8, No. 8, pp. l342-l346, Aug. 1956, Pat. Off. Sci. Lib.

Primary Examiner-Jay H. Woo Attorney, Agent, or Firm-Timothy L. Burgess;David A. Roth [5 7] ABSTRACT Melt blown 'non-woven mats prepared fromthermoplastic polymer fibers and substantially completely free ofpolymer shot are produced at high polymer throughput rates in animproved melt blowing process in which thermoplastic polymer resins,preferably polypropylene, having initial intrinsic viscosities of atleast 1.4,.are degraded, optionally in the presence of a free radicalsource compound, to have both reduced intrinsic viscosities and anapparent viscosity in the melt-blowing nozzle orifices of from about 50to about 300 poise.

37 Claims, 4 Drawing Figures MATTING TO COLLECTION POINYPATENTEL%10Y19|9?4- $349,241

SHEETZUF 2 AIR PLATE HE'ATER SLOT FOR END PLATE 29 NON-WOVEN MATS BYMELT BLOWING CROSS REFERENCE TO RELATED APPLICATION This is acontinuation-in-part of Ser. No. 865,105 filed Oct. 9, 1969 and now U.S.Pat. No. 3,755,527 and entitled Melt Blown Non-Woven Synthetic PolymerMat Having High Tear Resistance, and also Ser. Nos. 103,050 and nowabandoned and 103,094 and now abandoned, each filed on Dec. 31, 1970,and entitled Non-Woven Mats by Melt Blowing, each of Ser. Nos. 103,050and 103,094 in turn being a continuation-inpart application of Ser. No.786,122 filed Dec. 23, 1968, and now abandoned, entitled Non-WovenPolypropylene Mat by Melt Blowing.

BACKGROUND OF THE INVENTION This invention relates to melt-blowingprocesses for producing non-woven mats. More particularly, it relates toprocesses in which a fiber-forming thermoplastic polymer resin isextruded in molten form through orifices of a heated nozzle into astream of hot gas to attenuate the molten resin as fibers which form afiber stream, the fibers being collected on a receiver in the path ofthe fiber stream to form the non-woven mat.

Various melt-blowing processes of the foregoing description have beendescribed heretofore, earlier efforts including those of Hall (U.S. Pat.No. 2,374,540), Manning (U.S. Pat. No. 2,411,659; U.S. Pat. No. 2,411,660; and U.S. Pat. No. 2,437,263) and Marshall (U.S. Pat. No.2,508,462). A melt-blowing process is disclosed in the articleSuper-Fine Thermoplastics,. by Van A. Wente, in Industrial andEngineering Chemistry, Volume 48, No. 8 1956), pages 1,-3421,346 andalso in Naval Research Laboratory Report No. 1 1 1437, submitted Apr.15, 1954, entitled Manufacture of Super-Fine Organic Fibers. The NavalResearch Laboratory process is further described in NRL Report 5265,dated Feb. 11, 1959, and entitled An Improved Device for the Formationof Super-Fine, Thermoplastic Fibers. U.S. Pat. No. 3,532,800 to Wyly etal discloses a use of the Naval Research Laboratory melt-blowingprocess. A melt spinning and blowing process is disclosed in BritishPat. No. 1,055,187 and U.S. Pat. Nos. 3,379,81 l and 3,502,763. Asevidenced by these prior melt-blowing processes,it has been believed andtaught that degradation of a fiber-forming thermoplastic polymer resinis to be avoided in a melt-blowing process.

Heretofore, non-woven mats made of essentially discontinuous fibers andproduced by known meltblowing processes have contained undesirablecoarse shot or beads of material larger than about 0.3 millimeter indiameter. Moreover, prior melt-blowing processes operate at low andgenerally uneconomical resin flow rates of less than 1.0 gram per minuteper resin outlet and experience difficulty in producing soft, fine, highquality mats that do not contain coarse shot. Also, earlier melt-blowingprocesses do not disclose how to produce mats substantially free ofcoarse shot from a fiber-fonning thermoplastic polymer resin having ahigh intrinsic viscosity (1.4 or greater), particularly with C -Cpolyolefins, especially polypropylene. These polyolefins, which areconventionally produced in the presence of a heterogeneous solidcatalyst, normally have very high intrinsic viscosities typically 2.2 to4 and higher, corresponding to high viscosity average molecular weightsof about 270,000 to about 550,000 and higher. Intrinsic viscosities asused herein are measured in decalin at 135 C. The melt flow rates ormelt indexes of these high intrinsic viscosity resins are quite low,typically about 5 to 0.5 and lower.

SUMMARY OF THE INVENTION Non-woven mats prepared from thermoplasticpolymer fibers are produced at unusually high polymer resin throughputrates with no adverse affects on mat quality, for example, withouthaving coarse shot greater than 0.3 millimeter in diameter in the mat,by an outstandingly improved melt-blowing process which this inventioncomprises. This improved process involves controlling within criticalranges the interrelationships of the parameters of polymer resin flowrate, polymer apparent viscosity, process temperatures, and gas flowrates. Polypropylene is a preferred polymer.

DESCRIPTION OF THE INVENTION The present invention is an improvement inmeltblowing processes for producing non-woven mats in which afiber-forming thermoplastic polymer resin is extruded in molten formthrough orifices of a heated nozzle into a stream of a hot inert gas to.attenuate the molten resin as fibers which are then collected on areceiver to form the non-woven mat.

It has been discovered that the production of high quality non-wovenmats of thermoplastic polymer fibers requires a prior degradation of thefiber-forming thermoplastic polymer resin so that the degraded resin,during extrusion through the resin orifices in the nozzle of themelt-blowing apparatus, has an apparent viscosity of from about 50 toabout 300 poise, measured at a shear rate of from about 700 to about3,500 sec.

It has been particularly discovered that fiber-forming thermoplasticpolymer resins which, as made, have high intrinsic viscosities (at leastabout 1.4) and low melt flow rates (at most about 55), can be employedin melt-blowing processes to produce melt-blown nonwoven mats of highquality, particularly non-woven mats which are substantially completelyfree of coarse shot having a diameter greater than 0.3 millimeter. To

use such high intrinsic'viscosity, low melt flow rate thermoplastics forthis purpose, it is first necessary, be-

fore extruding the resin from the nozzle orifices, to subject thethermoplastic polymer resin to a critically controlled degradation,optionally promoted by a free radical source compound, until thethermoplasticpolymer resin has both a reduced intrinsic viscosity offrom about 0.6 to less than about 1.4, preferably within the range fromabout 0.8 to about 1.3, advantageously from about 0.9 to about 1.2, andalso an apparent viscosity in the nozzle orifices during extrusion offrom about 50 to about 300 poise, preferably at least poise,advantageously from about 100 to 200 poise, measured at a shear rate offrom about 700 to about 3,500 sec".

This controlled prior degradation of initially high intrinsic viscosityfiber-forming thermoplastic polymer resins permits the production of newmelt-blown nonwoven mats of high quality which are of two types. Onemelt-blown non-woven mat is comprised of essentially continuous fibershaving diameters in the range from about 8 to about 400, preferably fromabout 8 to about 50 microns, and is substantially completely free ofshot, both coarse and fine. The other type of melt-blown non-woven matis comprised of discontinuous fibers having diameters in the range fromabout 0.5 to about 5 microns, preferably from about 0.5 to about 2microns, and contains only very fine shot, less than 0.3 millimeter indiameter. Both types of these non-woven mats that are substantiallycompletely free of coarse shot have less than about 1 weight percent,preferably less than 0.5 weight percent of shot having diameters largerthan 0.3 millimeter. The latter type of mat may contain from about 5about 25 weight percent of shot with diameters in the range of about 0.2to about 0.1 millimeter, less of such shot being acceptable as shot sizeincreases. Preferably shot size is less than 0.1 millimeter. (Shot sizerefers to shot in the as made form, prior to any calendering orcompression thereof which tends to flatten the shot and increase itsdiameter.) The intrinsic viscosity of the fibers in these mats is in therange from about 0.6 to less than about 1.4.

Successful production of these high quality mats involves carefulselection of special process conditions and a correlation of theapparent viscosity of the degraded resin with the resin flow rates ofthe degraded resin and with gas fiow rates, which occur both in a lowgas flow rate regime of from about 2.5 to about pounds per minute persquare inch of gas outlet area and in a high gas fiow rate regime offrom more than 20 to about 100 pounds per minute per square inch of gasoutlet area. The selection and correlation of these special processconditions is described hereinafter in greater detail. It is appropriatefirst, however, to describe in greater detail the process of degradingthe initially high intrinsic viscosity fiber-forming thermoplasticresins employed in the subject process.

There are a few general approaches to bring about the extent of polymerdegradation requisite to the practice of this invention. Temperatureswell above the melting point of the polymer are employed. In the absenceof free radical source compounds, which promote oxidative degradation,the high intrinsic viscosity resin suitably is subjected to atemperature within the range from about 550 F. to about 900 F.,preferably from about 600 F. to about 750 F., for a period of timeeffective to cause the requisite extent of resin degradation, typicallyfrom about 1 to about 10 minutes, preferably from 2 to about 6 minutes.No effort is made to exclude oxygen from the thermal degradationreaction. Accordingly, both thermal and oxidative degradation occur insuch temperature ranges, oxidative degradation being predominate attemperatures below about 650 F., and thermal degradation becomingpredominate above about 650 F. (The activation energy for autooxidativedegradation is reported to be from about 26 to about 33 Kcal/mol; forthermal degradation it is reported to be from about to about Kcal/mol;for a combined thermal and oxidative process, it is calculated to beabout 33 Kcal/mol. Thus, at 550 F., the percent of the total degradationreaction attributable to autooxidation is about 90 percent; at 600 F.,it is about percent, and at 650 F., it is about 55 percent.) Thus,herein, oxidative degradation will be understood to be occurring,particularly at the lower temperatures in the aforesaid temperatureranges, whenever thermal degradation is mentioned. Lower temperatures offrom about 475 F. to about 650 F. are suitably employed to bring aboutdegradation when oxidative degradation is promoted by the presence ofone or more free radical source compounds.

Suitable free radical source compounds include organic peroxides, thiylcompounds-(including thiazoles and thiurams, thiobisphenols andthiophosphites) and organo-tin compounds. Preferred free radical sourcecompounds include t-butylbenzoate, dicumylperoxide,2,5-dimethyl-2,5-di-tert-butylperoxy3-hexene (Lupersol 130), a,a-bis(tert-butylperoxy) diisopropyl benzene (Vul Cup R), or any otherfree radical source compounds having a lO-hour half life temperatureover C., or mixtures thereof. In general, the higher the decompositiontemperature of the free radical source compound, the better. Referenceis made to pp 66-67 of Modern Plastics, November l97l, for a morecomplete list of suitable such compounds. Sulphur compounds which giverise to suitable thiyl compounds are disclosed in US. Pat. No.3,143,584. Suitably such free radical source compounds are used atconcentration in the range from about 0.0] to about 5 weight percent,preferably from about 0.1 to about 3 weight percent.

The thermoplastic polymer resin having the high initial intrinsicviscosity of at least L4 is preferably thermally and/or oxidativelydegraded either in an extruder separate from the melt-blowing apparatusor in an extruder feeding the resin into the nozzle orifices of themelt-blowing apparatus. Altematively, the requisite extent ofdegradation may be imparted to the resin by thermal degradation of theresin in the heated nozzle. Preferably, however, the requisite extent ofdegradation is imparted to the resin at least partially in the extruderfeeding the resin into the nozzle orifices.

The degraded fiber-forming thermoplastic polymer resin used in thepresent melt-blowing process preferably is produced, in one or moredegradation treatments, from fiber-forming thermoplastic polymer resinsthat are degradable to have an apparent viscosity in the nozzle orificesof from about 50 to about 500 poise, including polyamides, e.g.,poly(hexamethylene adipamide), poly(m-caproamide) and poly(hexamethylenesebacamide); polyesters, e.g., poly(methymethacrylate) andpoly(ethyleneterephthalate): polyvinyls, e.g., polystyrene; C -Cpolyolefins, high density polyethylene, and mixtures thereof. Preferablythe fiberforming thermoplastic polymer, as made, has an intrinsicviscosity of at least about 1.4, most preferably about 2.5 and greater.Supported metal oxide or Ziegler transition metal halide catalyzedolefin polymers, especially the C -C polyolefins having initial minimumintrinsic viscosities of 1.4 and greater, are preferred, particularlyfiber-forming polypropylene. In accordance with this invention,commercially useful resin throughput rates can be utilized. Suitableresin throughput (flow) rates range'from nominally about 0.1 (e.g. aslow as about 0.07) to about 5 grams per minute per nozzle orifice,preferably at least about 1 gram per minute per orifice.

In the melt-blowing process of the present invention, the degradedfiber-forming thermoplastic polymer resin is attenuated while stillmolten to fibers having diameters of 0.5 to 400 microns. The diameter ofthe attenuated fibers will decrease as the gas flow rate through the gasoutlets or slots on either side of the nozzle die openings increase. Gasrates may vary from 2.5 to 100 pounds per minute per square inch of gasoutlet area, or greater. At low to moderate gas rates of from about 2.5to about 20 pounds per minute per square inch of gas outlet area forresin flow rates of from about 0.1 to about 5 grams per minute perorifice,

the fibers are essentially continuous with little or no fiber breaks.Fibers produced in this low to moderate gas flow rate regime havediameters of from about 8 to about 200400 microns, preferably from about8 to about 50 microns.

As gas rates increase for a selected resin flow rate of a degradedresin, the number of fiber breaks increase, producing coarse shot, whichis large globs of polymer having a diameter at least several times thatof the average diameter size of the fibers in the mat and at least 0.3millimeter in diameter. The production of coarse shot is objectionablein the mat when a uniform mat is desired. Further, if the mat iscalendered or further treated, the coarse shot will produceimperfections in the surface or even holes.

At high gas rates of from about more than to about 100 pounds per minuteper square inch of gas outlet area, the mats are composed ofnon-continuous polymer fibers with the presence of a fine shot less than0.3 millimeter, preferably 0.1 millimeter in diameter, which is notobjectionable in the mat. At the high air rates for resin flow rates inthe range from about 0.1 to about 5 grams per minute per orifice, matsare pro duced in which the fiber size is between about 0.5 and 5microns.

The resin flow rate, gas flow rate and the apparent viscosity of thedegraded resin are controlled and correlated, in accordance with theinvention, to provide increased production of melt-blown non-woven matswhile preventing the inclusion as aforesaid of coarse shot in the mats.These correlations make use of interrelationships which exist betweenthe resin flow rate, gas flow rate and apparent viscosity of thedegraded resin in both the high and low gas flow rate regimes. Theseinterrelationships are illustrated in Table I which TABLE I and gas flowrate in the aforementioned range are apparent viscosity above which,forthe chosen combination of resin flow rate and gas flow rate, coarseshot is formed.

If it is wished to increase or decrease in the values of one of thevariables in the chosen combination, an adjustment may need to be madein the third variable to prevent the formation of coarse shot. Forexample, in the first case in which resin flow rate and gas flow rateare the chosen combination, if the gas flow rate is increased or theresin flow rate is decreased, the minimum apparent viscosity selectedfor the degraded resin must be increased in the low gas flow rate regimeto prevent the inclusion of coarse shot in the resultant nonwoven mat.However, no limiting adjustment is necessary in the apparent viscosityto prevent the inclusion of coarse shot in the mat in the low gas flowrate regime if the gas flow rate is decreased or the polymer rate isincreased; in this situation, the result in the low gas flow rate regimewill be thicker, coaser fibers. In the high gas flow rate regime, adecrease in the gas flow rate or an increase in the resin flow raterequires a decrease in the maximum apparent viscosity of the degradedresin in order to prevent the inclusion of coarse shot in the non-wovenmat. However, no limiting adjustment in apparent viscosity is necessaryto prevent the inclusion of large shot in high gas flow rate regimeInterrelationships of Resin Flow Rate (RFR), Gas Flow Rate (GFR) andApparent Viscosity (A.V.) of Degraded Resin in High and Low GFR RegimesThird Third Variable Limiting Adjustment: A. Chosen Combination of TwoVariables Variable Low GFR Regime High GFR Regime l. RFR, GFR A.V.Minimum Maximum 2. RFR., A.V. GFR Maximum Minimum 3. GFR, A.V. RFRMinimum Maximum B. Fixed Changed l. RFR GFR (increase A.V. (increase(decrease (decrease GFR RFR (increase A.V. (decrease (decrease (increase2. RFR A.V. (increase GFR (increase 1 (decrease (decrease A.V. RFR(increase GFR (increase (decrease (decrease 3. GFR A.V. (increase RFR(decrease (decrease (increase A.V. GFR (increase RFR (increase (decrease(decrease Table I shows that there are three basic groupings of thevariables. For a particular combination for values for two variableswhich it is chosen to fix, the third variable has, in the low and highgas flow rate regimes, either a minimum value below which, or a maximumvalue above which, coarse shot will be formed. Thus,

referring to Group 1, where a particular resin flow rate ,7

if gas flow rate is increased or resin flow rate is decreased; in thissituation the fibers in the non-woven mats generally have smallerdiameters.

The foregoing interrelationships will be further understood by thedescription of the preferred embodimerit and modes of the inventiontaken with the examples.

BRIEF DESCRIPTION OF THE DRAWINGS I FIG. 1 is a schematic view of theoverall melt-blowing process;

FIG. 2 is a detailed exploded oblique view of a nozzle die which may beused in the melt-blowing process;

FIG. 3 is a cross-sectional view of the nozzlie die; and

FIG. 4 is a view of the lay-down of melt-blown fibers on a pick-updevice.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of thedrawings, a fiber-forming thermoplastic polymer resin having anintrinsic viscosity of at least about 1.4, preferably a C to Cpolyolefin, e.g., poly propylene, is introduced into a pellet hopper 1of an extruder 2. The resin used in the present invention has eitherbeen thermally degraded before being introduced into the extruder 2 oris thermally degraded in the extruder 2 and/or die head 3 with orwithout the use of free radical source compounds. According to thepresent invention, the resin is added into the hopper l and then isheated in the extruder 2 at temperatures in excess of about 550 F. andpreferably within the range of 600 to 800 F. The degree of thermaldegradation necessary varies since the viscosity average molecularweight of the resin will vary in conventional production of variousresins having intrinsic viscosities of at least 1.4, and further sincethe degree of thermal degradation will depend on the resin flow ratesused in the melt-blowing process. Particularly in the instances ofpolyolefins produced in a Ziegler catalyzed process, it has been foundthat a requisite degree of thermal degradation is necessary before itcan be utilized in the melt-blown process of the present inven tion. Thefiber-forming resin is forced through the extruder 2 by a drive 4 intothe nozzle die head 3. The nozzle die head 3 may contain a heating plate5 which may also be used in the thermal degradation of the resin beforeit is melt-blown. Thus, a partial thermal degradation of the resin maybe carried out in extruder 2 and a final thermal degradation may beperformed in the nozzle die head 3. The resin is then forced out of arow of nozzle orifices or die openings 6 in the nozzle die head 3 asmolten strands into a gas stream which attenuates the molten strandsinto fibers 7 which are collected on a moving collecting device 8 suchas a drum 9 to form a continuous mat 10. The gas stream which attenuatesthe extruded molten resin is supplied through gas outlet slots 11 and12, respectively. These gas slots 11 and 12 are supplied with a hotinert gas, preferably air, by gas lines 13 and 14, respectively. Theterm inert in respect to the hot gas is used to mean a gas which is nomore reactive with the extruded molten resin at the gas temperaturesdescribed herein than air is at such temperatures. The examplesdisclosed herein use air as a gas.

The air temperatures may vary from 500 to 900 F. Generally the airtemperatures are within the same temperature range as the nozzle dietemperatures. Usually the air temperatures are slightly higher, about 50F., than nozzle die temperatures.

The process may be further understood by considering the details of thenozzle die head 3 which is more fully set forth in FIGS. 2 and 3. Thecomplement parts of the die head 3 are shown in FIG. 2 in the explodedview. The nozzle die head 3 is made up of upper die.

v through an inlet 17. The resin then goes into a chamber 18 between theupper and lower die plates 15 and 16, respectively. The facing of thedie plate 16 has milled grooves 19 which terminate in the nozzle dieopenings or orifices 6. It is understood, of course, that the milledgrooves may be in the lower die plate 16, in the upper die plate 15, orgrooves may be milled in both plates 15 and 16. Alternatively orificesmay be drilled in a single plate. An upper gas cover plate 20 and alower gas cover plate 21 are connected to the upper die plate and lowerdie plate 15 and 16, respectively. The hot gas is supplied by inlets 25and upper air plate 20 and lower inlet 26 in lower gas plate 21.Suitable baffling means (not shown) may be provided in both the uppergas chamber 27 and lower gas chamber 28 to provide a uniform flow of gasthrough the gas slots 23 and 25, respectively. End plates 29 and 30 makeup the remainder of the nozzle die head'3. As shown in FIG. 3, the rearportion of the die head 3 may contain heating means 5 for heating boththe polymer and air in the nozzle die head 3.

In FIG. 4 the laydown of the attenuated fibers 7 on the drum 9 is shownin more detail. The fibers are blown from the nozzle die head 3 and arelaid down on the screen covering drum 9 which preferably is positionedfrom I to 30 inches from the nozzle orifices 6 in the nozzle die head 3.Mats produced when the screen is at a distance of 1% to 2 inches differin compactness and appearance from those produced at a distance of 5 to8 inches or those collected at greater than 12 inches. Also illustratedin FIG. 4 is the production of shot 31 which may be produced in the mat10. Shot" is a mass or glob of polymer which appears to be the result ofindividual fibers breaking, such a fiber break illustrated at 32 whichbecause of its attenuation is forced into the mat 10 as a glob with adiameter many times the average diameter of the fiber.

The production of shot is related to gas flow rates at any given resinflow rate for a degraded resin apparent viscosity. Also, in making auniform web, it is desired to eliminate the formation of rope. Rope"occurs when the gas flow rates from the two slots 11 and 12 are out ofadjustment such that the attenuated fibers come in contact one with theother and are not blown away from the nozzle die head as individualfibers but come in contact and are laid down as collected aggregates.lnsufficient gas flow rates for the resin flow rate or having the gasflow rates from the upper or lower gas slots out of adjustment willproduce rope in a nonwoven mat. Rope can also be formed at long nozzledie heat-to-collecting device distances (2 to 3 feet) where the fibersare entangled due to the turbulence of the air jet. The presence of bothrope-and coarse shot will make a non-woven material unacceptable formany uses because of adverse effect on appearance and on strengthproperties.

As the gas flow rates for a fixed resin flow rate are increasedsufficiently so that ropeis not formed, mats are formed from essentiallycontinuous fibers, and have essentially no coarse shot, i.e., less thanabout I weight percent shot. This occurs at gas flow rates in the rangefrom about 2.5 to about 20 pounds per minute per square inch of totalslot area. With increasing gas flow rates for the fixed polymer rate andapparent viscosity, a maximum gas flow rate is exceeded and coarse shotis produced having diameters greater than 0.3 millimeter. As the gasflow rates increase even further, in the range of from more than 20 toabout 100 pounds per minute per square inch of total slot area, the shotbecomes smaller and often elongated and appears as very fine shot athigh gas flow rates. Shot is coarse and unacceptable when the masses orglobs of polymer are relatively large (greater than 0.3 millimeter indiameter) and can be seen with the eye or when the web is calendered asan imperfection or fused spot.

The level of thermal treatment appropriate to impart the requite extentof thermal degradation to the feed resin, in the extruder 2 for a setnozzle die temperature and a set resin flow rate is readily determined.The nozzle die tip temperature is set in the range from abut 500 F. to900 F., preferably 500 F. to 750 F., and the resin flow rate is set fromabout 0.1 to about grams per minute per nozzle orifice. Then the airflow is fixed at a rate which is in the range of from more than to about100 pounds per minute per square inch of the total air slot area (sonicvelocity levels). The mat is observed as zones of the extruder areheated. At too low a temperature in the extruder 2 the mat contains manylarge blobs of polymer and/or coarse ropey material. As the temperatureis increased, the apparent viscosity of the degraded resin exceeds theminimum for the chosen resin flow rate and air flow rate and the matbecomes finer fibered, softer, and has less and smaller shot of diametersmaller than 0.3 millimeter. When the temperature is too high, the matbecomes extremely soft and fluffy, but the air blast from the die causesextreme fiber breakage and many short fibers to be blown from the matinto the air, away from the laydown zone. The mats produced in theappropriate thermal degradation range are very white, opaque, and soft.The fibers are between abut 0.5 and 5 microns diameter, diameter,usually between about 1.5 and 4 microns in diameter.

As an alternative procedure, the temperature of the extruder 2 can befixed, and the appropriate extent of thermal degradation can be obtainedby raising the nozzle die temperature until it is in the correct rangeto produce the fine fibers and acceptably small fine shot, withoutextreme fiber breakage.

The best conditions for a fine fibered, soft web are obtained at athermal treating temperature which is just below the temperature wherefine fibers escape from the laydown zone with the air stream. The bestthermal treating temperature for obtaining the highest strength fibersis the lowest temperature at which the shot is unobjectionable. Theexact treating temperatures required to obtain good fine fibered webs isdependent upon the starting resin and the rate of throughput of theresin in the extruder. For example, a 5 melt flow rate (2.23 intrinsicviscosity) resin may require tempera tures in the range of 650-700 F.while an 0.5 melt flow rate (3.49 intrinsic viscosity) resin may requiretemperatures of 700-760 F. or higher. Thermal treatment of the resin,say to intrinsic viscosities of from about 1.30 to 1.25, prior tofeeding the resin through the extruder 2 can lower the requiredtemperatures in the extruder 2 and/or the nozzle die head 3.

Another indication that the thermal treatment is adequate is the resinpressure (resin pressure head in the nozzle orifices) for the resin flowrate in the nozzle die head 3. When the resin is correctly thermallytreated in the extruder, the resin pressure lies in a small rangeindependent of the melt flow rate or intrinsic viscosity of the startingresin or of the nozzle die temperature. In the terms of the particulargeometry of the nozzle die holes 6, by measuring the pressure'upstreamof the nozzle die holes for the flow rate of the particular resin and bycalculating the apparent viscosity of the degraded resin in the nozzledie holes 6 according to methods well known in polymer rheology [see,e.g., H. V. Boenig, Polyolefins, p. 264 (i966) and Chemical EngineeringHandbook (Perry ed. 1950), p. 375], thermal treatment produces anapparent viscosity in the nozzle die holes 6 of from about 5 0 to about300 poise 'prefe 5 ably atTeast I00 poisefan specially preferred rangebeing from about 100 to about 200 poise.

With the appropriate level of thermal treatment determined as describedimmediately above for the particular starting resin and resin flow rate,the air flow rate is suitably decreased tothe low air flow rate regime(from about 2.5 to about 20 pounds per minute per square inch of totalair slot area) for the production of non-woven mats in the low air flowrate regime from resin.

Non-woven mats produced in the low air flow rate regime consistessentially of continuous fibers whose morphology as seen by apolarizing microscope is nonoriented. If the fiber cools slowly, a largespherulitic structure can form and the fibers are stiff and brittle.With more rapid cooling, the fibers are non-spherulitic, flexible, andhave a high elongation to break. The cooling rate increases withdecreasing fiber size and increased die nozzle to collector distance.The table below shows upper limits of air flow rates for various polymerrates from about 0.1 to about 0.3 grams per minute per orifice forvarious nozzle die temperatures. As the gas (air) rate was increased,the fibers were observed with a stroboscopic light at about 600 cyclesper minute to observe visually when breakage started. The

maximum air flow rate just below the breakage point is recorded.

Die Nozzle 4-inch row of 80 resin extrusion orifices, each orifice .022inch diameter. .050 inches between orifice centers.

Air Slots 4 inches long above and below the row of nozzle orifices. theslot opening being varied as shown in the table. Resin Polypropylene,partially thermally degraded to a melt flow rate of 33 1.55 intrinsicviscosity).

Extruder Constant at 500 F.

Temperature Resin Flow Air Air Rate Nozzle Rate Slot Air lb/min/in Die(gm/min/ Height Velocity of Total Run Temp. F. orifice) (inches)(ft/sec) Slot Area 1 582 0.089 .0l2 293 4.5

the appropriately thermally degraded fiber-forming- Continued Resinl'luw Air Air Rate Nozzle Rate Slot Air lb/min/in Die (gm/min/ HeightVelocity of Total Run Temp. F. orifice) (inches) (ft/sec) Slot Area o Bycomparing Runs 1 through 7, it is seen that at constant nozzle dietemperature, the allowed air velocity increases as the polymer rateincreases.

By comparing Runs 8 with l and 2, 3 with 9. and 7 with 6, it is seenthat the allowable air velocity decreases as the nozzle die temperatureincreases.

Similar behavior is observed for all C -C polyolefin resins having anintrinsic viscosity of at least 1.4 that are appropriately thermallydegraded to intrinsic viscosities of from about 0.6 to less than 1.4.The air velocity which causes fiber breakage is well below the sonicvelocity of air at the nozzle die tip temperatures. The maximum fibervelocity as calculated from the fiber diameter and resin flow rate iswell' below the air velocity. The products consist of continuous fiberswhose diameters usually range from about 8 to 50, preferably 8-30microns depending onthe nozzle die temperature, air flow rates, resinflow rates, and degree of thermal degradation imparted to the resin. Thenonwoven mat or web has a slightly harsh feel and individual fibers arereadily seen with the eye or with a lowpowered magnifier (7X). The webs,when collected 6 or more inches from the die, show low strength and highelongation.

It is therefore seen that for resin flow rates of from about 0.1 toabout grams per minute per orifice, the characteristics of the non-wovenmat under appropriate thermal treatment conditions are largelydetermined by the gas (air) flow rates used in the meltblowing process.When the air flow rates are generally low or subsonic (2.5 to 20 poundsper minute per square inch total gas slot area), the fibers in thenonwoven mat are essentially continuous while at the high air flow ratesor sonic velocities the fibers are noncontinuous and in addition fineshot is produced.

Another factor determining the characteristics of the product mat is thedistance of the take-up device from the openings 6 in the nozzle diehead 3. When the collecting device is between 1 to 6 inches. there isconsiderable self-bonding of the fibers since they are still hot at thepoint of laydown so that they bond one to another upon contact. Atdistances of 6 inches there still occurs self-bonding, but the amountdecreases with distance.

When the air flow rates are too low for a selected resin flow rate,large coarse fibers are formed. These fibers are generally entwined toform coarse, ropey bundles or rope in the mat resulting in a coarse,nonpliable, brittle mat structure. At low to moderate air flow ratesappropriate for the selected resin flow rate, fine, continuous fibers(most preferably 8 to 30 microns in diameter) are produced and the matis of a soft and pliable texture. The mats produced at these moderateair rates have a cardboard appearing rigidity when the fibers arecollected at about 5 to 6 inches but have loose fiber whiskers on themore compact inner structure of the mat. If the fibers are collectednearer the'die openings, the mats appear more rigid and with less loosefibers or whiskers. A fluffier mat is produced if the fibers arecollected at over 5 to 6 inches.

At even higher air flow rates for the selected resin flow rate, fiberbreakage occurs resulting in large objectionable shot in the mat. Thistype of shot is intermittent and may be as large as 1 millimeter indiameter and gives a rough, sandpapery feel to the mat. Upon calenderingthe mat, this type of shot appears as large translucent areas in the matgiving a coarsely speckled appearance to the calendered mat.

At even higher air flow rates for the selected resin flow rate (in therange from about 20 to about 100 pounds per minute per square inch oftotal air slot area), essentially all non-continuous and very finefibers are produced with the formation of a very fine uniform type ofshot. This shot is less than 0.1 millimeter in diameter and is notnoticeable to the touch nor visually, but is detected after calenderingwhereupon the mat appears as a very smooth white mat with a highlyuniform fine grained texture due to the presence of the very fineparticles of shot. The mat produced at these very high air rates and atlong die-to-collector distances has a very soft and pliable texturewhich appears like cotton batting, due to the very fine fibers (lessthan 5 microns).

The present invention will be further illustrated by the followingspecific examples which are given by way of illustration. In theexamples, unless otherwise specified, the nozzle die used was a 4-inchrow of orifices for resin extrusion, each orifice having a .022 inchdiameter and being..050 between centers. The air slots above and belowthe row of orifices had a nominal height of about 0.010 inch.

EXAMPLES 14 In these examples the conditions were as follows:

Resin 33.6 melt flow rate (1.54 intrinsic viscosity) polypropyleneExtruder Temperature 590 F.

Die Temperature 530545 F.

Air Temperature 510540 F.

Resin 7.1 gms/min (0.089 gms/min/orifice) Collector Distance 8 inchesCollector. rpm 0.9

These Examples demonstrate the importance of proper air flow rate inobtaining mats with desirable characteristics. The optimum air flow ratewill, of course, vary depending on other conditions.

TABLE n EFFECT OF AIR RATE ON FIBER FORMATION icles. Mat rough and ofpoor appearance.

TABLE III MAT PRODUCTION AT VERY HIGH AlR RATE Air Rate A Example No.pounds/min pounds/min/in slot Mat Description 1.05 13.1 Mat containslarge shot, rough.

poor appearance 6 1.28 16.0 Mat contains smaller shot, still 7 1.5118.85 I Still smaller shot, better appearancev 8 1.74 21.8 Mat containsfine shot. Good appearance 9 2.09 26.1 Very fine shot unnoticeable toFor example, with all conditions the same as in the above except at aresin flow rate which was 21.2 grams per minute (0.265 grams per minuteper orifice), an air flow rate of 1.12 pounds per minute (14 pounds/min-/in slot) gave the best mat as compared to an air rate of 0.659pounds/min. (8.25 pounds/min./in slot) in Example 3. At thishigherpolymer rate, the fiber sizes were larger but still a good, uniformshot-free soft mat was obtained.

Moreover in an example using a die temperature of 590 F. instead of530-545 F. of Example 3,'an air rate of 0.59 pounds/min. (7.36poundslmin/in 'slot) produced the best mat. It is generally true that ahigher die temperature requires lower air flow rates for high qualitymats.

EXAMPLES 5-9 The following Examples illustrate the mats that can beproduced at very high air rates, where the size of the 7 shot formed isso small as to be undetectable. The condit on w re .asfdbws Air rate wasvaried with the results shown in Table III;

the touch. Mat extremely soft and pliable. Excellent appearance EXAMPLES10 13 The following Examples show that different base resins can be usedfor forming good quality mats by proper thermal treatment of the resinusing elevated extruder and die temperatures prior to fiber formation.For Examples 10-12 the conditions were as follows:

' Resin 0.6 melt flow rate (3.37

intrinsic viscosity polypropylene Air Temperature 640 F. Resin Flow Rate8.2 gms/min.

Air Rate 0.54 pounds/min.

- (6.75 pounds/min/in slot) Collector Distance 6 inches Collector. rpm1.0

For Example 13 the conditions were as follows;

Resin 3.0 melt flow rate (2.47

intrinsic viscosity) polypropylene Air Temperature 580 F. Resin FlowRate 7.2 gms/min.

Air Rate 0.786 pounds/min.

(9.83 pounds/minJin slot) Collector Distance 7 inches Collector. rpm 30The extruder temperatures and die temperatures used 2 P9EEi2lab r-.l!

TABLE IV EFFECT OF THERMAL TREATMENT ON FIBER FORMATION Example No.

no shot. soft and pliable TABLE IVCntinued 7 EFFECT OF THERMAL TREATMENTON FIBER FORMATION Example N0. Extruder Temp. F. Die Temp. F. MatDescription 12 W A I V m 680 0 650 Appreciable shot in mat. 13 600 740Soft, pliable, and

shot-free mat.

As seen in Examples -12, the extruder tempera- 10 The mat from Example14 was soft and pliable with ture is critical, holding all otherconditions the same, in thermally treating this low melt flow resin soas to produce soft, shot-free mats. However, Example 13 illustrates thata lower extruder temperature but higher die temperature was used to forma good quality mat.

EXAMPLES 14-19 In the foregoing examples, the variables in the processare illustrated and emphasized; however, the following examples are setforth to illustrate the variety of mats which may be produced. The matsmay be made in a wide variation of thickness, degrees of rigidity andgeneral appearance. All the mats of the present invention havesufficient thickness, rigidity and strength to be self-supporting suchthat it may be removed from the take-up device as a self-bonded mat.

Mats may be produced which are tissue paper thin (0.0005-0003 inch) andwould drape over a pencil in the same manner. Thicker mats (0.05-0.5inch) while still soft and pliable may have a more rigid appearance,e.g. that of thin cardboard. The thickness of the mat may be increasedby slowing down the rate of removal of the mat from the take-up deviceor by multiple layers. The rate of removal may be controlled by the rpmof the drum while the multiple layers may be accomplished by multiplerotations of the drum or by using multiple die heads.

At the lower air rates, the mats have a more compact appearing core withloose, whisker-like fibers on either side of the more compact fibers.The compactness of the fibers in the mat is controlled largely by thedistance of the take-up device from the die openings. At the high airrates, the mats have the appearance of cotton batting.

Exemplary mats are illustrated in the examples set forth in Table Vwhich follows:

a compact core and loose fibers on each surface. The

mat had a rigidity or stiffness like thin cardboard. ln

contrast, the mat from Example 15 was produced at high air rates, theother conditions being very similar and was very soft, having theappearance of compacted cotton batting. The mat, due to its thickness,was fairly rigid.

The mat from Example 16 was approximately 0.0025 inches thick as takenfrom the pick-up device and when calendered had a translucent, slightlymottled, tissue paper appearance. The calendered mat was about 0.0009inches thick. The mat from Example 17 was approximately 0.0028 inchesbefore calendering. The calendered mat had a very fine grain, uniform,tissue paper appearance. i

The mat from Example 18 illustrates that multiple layers of fibers maybe melt blown to produce thicker mats. On the other hand, paper-likemats can be produced at very close distances from the die openings suchas illustrated in Example 19.

EXAMPLES 20 and 21 For some applications it may be desirable to useother polyolefins than polypropylene in the form of the fine fiber mats.For example, polybutene-l can give a much lower stiffness to the mat;poly-3-methylbutene- 1 poly-4-methylpentenel po1y-4-methylhexane-1 andp0ly-5-methylhexene-l have much higher melting points thanpolypropylene.

It'has been found that C or greater polyolefins having an intrinsicviscosity of at least about 1.5 can be melt-blown by the process of thepresent invention to produce good mats provided the C or greaterpolyolefins are appropriately thermally treated.

Basis wt. gm/m 17 To illustrate another C to C polyolefin other thanpolypropylene, po1y-4-methylpentene-l was successfully melt blown toproduce a fine fiber mat (0.5 to 5 micron diameter). The conditions usedin the melt blowing and the fiber characteristics are set forth in 5Table V1 hereinafter.

The extent of thermal treatment necessary to thermally degrade a feedpolypropylene resin having a starting melt flow rate of 33.6 (intrinsicviscosity of 1.54) to be extruded at a rate of 0.22 grams per minute perorifice from an extruder at a die temperature of about 600-610 F. wasdetermined by fixing the polymer flow rate and the nozzle dietemperature and then increasing the extruder temperature until largeshot (greater than 0.1 millimeters) was no longer produced yet short ofcausing fiber breakage. The data in Table M we. t k

D hole diameter (for non-circular holes 4-/P where A area of opening, P=wetted perimeter) p melt density g 32.2 lb ft/sec llb force AP= pressuredrop through hole L length of holes W=rate of melt flow through holeFrom the foregoing measured and calculated data, it is seen that at agiven resin flow rate, air flow rate, and nozzle die temperature, theextent of thermal treatment is very critical in order to produce anappropriate level of thermal degradation and appropriate viscosity inthe nozzle die holes. Thus, for the die hole configurations used inExamples 23-26 and at the polymer flow rate, air flow rate, and nozzledie temperature there employed, an extruder maximum temperature of 710F. was ineffective to reduce the viscosity in the die holes to a levelpreventing the formation of coarse shot, but at an extruder maximumtemperature of 732 F., the viscosity in the die holes had dropped belowpoise and the fibers produced were so weak that they could not beformedinto a satisfactory web. However, a shot free web of fine fibers wasproduced at an extruder maximum temperature of 722 F., which produced anapparent viscosity in the nozzle die hose of 63.6 poise.

The particular extent of thermal treatment necessary to degrade a feedresin to the proper intrinsic and apparent viscosity for extrusion at aparticular resin flow rate and die temperature will vary with thechanges in the die configuration, starting resin intrinsic viscosity, orresin flow rate. The necessary air rate will vary with the acceptableapparent viscosity in the nozzle die orifices. This is illustrated inthe following Examples 27-31.

EXAMPLES 27-31 In these examples, a 10-inch die with a row of 200 triangilarshaped orifices having a height of 0.15 inch was The above data wastaken using a 4-inch wide nozzle die head containing a row of 80triangular shaped orifices which were 0.015 inch in height and 0.75 inchlong, with air slots of 0.015 inch in height on each side of the nozzleorifices. The apparent viscosity existing in the nozzle orifices at aparticular extruder temperature was ealc ulated according to. thefollowing equation: a m =I pgc /l28 L W The process conditions utilizedin Examples 26-31 where and the results thereby obtained are set outbelow in 1.1,, apparent viscosity Table VlII.

TABLE Vlll Example 27 28 29 30 31 Maximum ExtruderTemp.,F. 638 639 770650 720 Air Temperature, F. 631 630 660 700 707 Die Tip Temperature. F.615 597 625 610 640 Air Flow Rate,

pounds/min/in slot 76 33.5 35 82 46 Polymer Resin Flow Rate TABLE VIII-Continued Example 27 2s 29 30 31 Melt Pressure. psig 275 175 170 2 30260 93 190 156 162 75 Calculated ,u., poise The higher die tiptemperature of Example 27 compared to Example 28 produced a lowerapparent viscosity of the resin in the orifice. In Example 27 theapparent viscosity was 93 poise, whereas the apparent viscosity in thenozzle orifice in Example 28 was 190 poise.

Comparison of Example 30 with Example 28 dis-' closes that a greateroverall extent of thermal treatment and higher air temperature wasnecessary for a doubled flow rate of the same starting resin to producea satisfactory level of thermal degradation.

Similarly, a greater degree of thermal degradation, i.e., higherextruder temperature, was necessary for the higher intrinsic viscositystarting resin of Example 29 in order to produce a satisfactory level ofthermal degradation.

The mats made by the process of the present invention are useful asfilters, wiping cloths, thermal insulation, battery separator basestock,packaging materials, hydrocarbon absorption material, diaper liners,synthetic leather base, laminates, sound absorbing materials, padding,disposable clothing components, bags, shipping protection, syntheticpaper and for electrical paper applications. The mats may be used asmeltblown or they may be pressed, calendered, cut impregnated, coated,laminated, or otherwise treated for particular end uses. In general, themats made of the fibers in the range from 0.5 to 5 microns have greaterstrip tensile strength than the mats made from the fibers having 8 to 40micron diameter fibers, such latter mats having generally greater tearresistances,

The term self-bonded as used herein means that the mats are coherent,integral structures capable of withstanding normal handling such aswinding, unwinding, cutting, pressing, calendering, etc., without losingtheir essential mat-like character. In most mats produced according tothe present invention, some thermal bonding occurs, usually directlydependent on the distance from the die head that the mat was formed.

The nature and object of the present invention having been described andillustrated and the best mode thereof now contemplated set forth, whatwe wish to claim as new and useful and secure by Letters Patent 1. In aprocess for producing a melt-blown nonwoven mat wherein a fiber-formingthermoplastic polymer resin is extruded in molten form from orifices ofa heated nozzle into astream of hot inert gas which attenuates saidmolten resin into fibers that form a fiber stream, and said fibers arecollected on a receiver in the path of said fiber stream to form saidnon-woven mat,

the improvement which comprises:

subjecting a fiber-forming thermoplastic polymer resin having an initialintrinsic viscosity of at least 1.4 to degradation in the presence of afree radical source compound prior to extrusion from said nozzleorifices until said resin has both a reduced intrinsic viscosity of fromabout 0.6 to less than L4 and an apparent viscosity in said nozzleorifices of from about 50 to about 300 poise.

2. The process of claim I wherein said resin is subjected to thermaldegradation at a temperature within the range from about 550 F. to about900 F. for a period of time effective to cause said resin to have saidreduced intrinsic viscosity and said apparent viscosity.

3. The process of claim 2 in which said thermoplastic polymer resin issubjected to said thermal degradation at least partially in an extruderfeeding said resin into said nozzle.

4. The process of claim 3 wherein said resin is thermally degraded in anextruder for from about I to about 10 minutes effective to cause saidresin to have said reduced intrinsic viscosity and said apparentviscosity.

5. The process of claim 1 wherein said free radical source compound isselected from organic peroxides, thiyl compounds, and organo-tincompounds.

6. The process of claim 1 wherein said thermoplastic polymer resin isselected from C -C polyolefins and mixtures thereof which have aninitial intrinsic viscosity of at least 1.4.

7. In a process for producing a melt-blown nonwoven mat wherein afiber-forming thermoplastic polymer resin is extruded in molten formfrom orifices of a heated nozzle into a stream of hot inert gas whichattenuates said molten resin into fibers that form a fiber stream, andsaid fibers are collected on a receiver in the path of said fiber streamto form said non-woven mat,

the improvement of producing said mat at high resin flow rates, whichcomprises:

extruding from said nozzle orifices, at a resin flow rate of from aboutat least 0.1 to about 5 grams per minute per orifice, a fiber-formingthermoplastic polymer resin degraded to have both an intrinsic viscosityof from about 0.6 to less than 1.4 and an apparent viscosity in saidnozzle orifices of from about 50 to about 300 poise.

8. The process of claim 7 wherein said apparent viscosity is from aboutto about 300 poise.

9. The process of claim 7 wherein said resin is subjected to saiddegradation at least partially in an extruder feeding said resin to saidnozzle.

10. The process of claim 9 wherein said resin is subjected to atemperature within the range from about 5 50 F. to about 900 F. for aperiod of timefrom about 1 to about 10 minutes effective to cause saiddegradation of said resin until said resin has said apparent viscosityand said intrinsic viscosity. 1

11. The process of claim 7 wherein said resin is selected from C -Cpolyolefins and mixtures thereof.

12. In a process for producing a melt-blown nonwoven mat wherein afiber-forming thennoplastic polymer resin in molten form is forced by anextruder through a row of orifices in a heated nozzle into a stream ofhot inert gas which is issued from outlets adjacent to said row oforifices so as to attenuate said molten resin into fibers which form afiber stream, and said fibers are collected on a receiver in the path ofsaid fiber stream to form said non-woven mat,

the improvement of increasing the production of said non-woven matswhile preventing the inclusion of coarse shot in such mats, by themethod which comprises in combination:

subjecting a fiber-forming thermoplastic polymer resin having an initialintrinsic viscosity of at least 1.4 to thermal degradation, at leastpartially in an extruder, for a sufficient time at a temperature withinthe range of from about 550 F. to about 900 F. effective to cause saidresin to have both a reduced intrinsic viscosity of from about 0.6 toless than 1.4 and an apparent viscosity in said nozzle orifices of fromabout 50 to about 300 poise, said heated nozzle having a temperaturewithin the range of from about 500 F. to about 900 F.,

operating said extruder so as to force said degraded resin in moltenform from said row of nozzle orifices at a resin flow rate of from about0.1 to about grams per minute per nozzle orifices, and

issuing said hot, inert gas at a temperature from about 500 F. to about900 F. from said outlets at a gas flow rate of from about 2.5 to aboutpounds per minute per square inch of outlet area, effective to attenuatesaid extruded degraded resin into fibers having diameters of from about8 to about 400 microns,

said resin flow rate being selected from rates in said resin flow raterange which are not below a minimum rate below which, for a chosencombination of gas flow rate and degraded resin apparent viscosity,coarse shot is formed,

said minimum resin flow rate increasing in its aforesaid range as saidgas flow rate is increased in its range or as said degraded resin has adecreased apparent viscosity in its range, or both.

13. The method of claim 12 in which said resin is selected from C to Cpolyolefins and mixtures thereof.

14. The method of claim 13 in which said resin flow rate is at least 1.0gram per minute per orifice and said apparent viscosity is from about100 to about 300 poise.

15. In a process for producing a melt-blown nonwoven mat wherein afiber-forming thermoplastic polymer resin in molten form is forced by anextruder through a row of orifices in a heated nozzle into a stream ofhot inert gas which is issued from outlets adjacent to said row oforifices so as to attenuate said molten resin into fibers which form afiber stream, and said fibers are collected on a receiver in the path ofsaid fiber stream to form said non-woven mat,

the improvement of increasing the production of said non-woven matswhile preventing the inclusion of coarse shot in such mats, by themethod which.

said heated nozzle having a temperature within the range of from about500 F. to about 900 F., operating said extruder so as to force saiddegraded resin in molten form from said row of nozzle orifices at aresin flow rate of from about 0.1 to about 5 grams per minute per nozzleorifice, and

issuing said hot, inert gas at a temperature from about 500 F. to about900 F. from said outlets at a gas flow rate of from greater than 20 toabout pounds per minute per square inch of outlet area effective toattenuate said extruded degraded resin into fibers having a diameter offrom about 0.5 to

I about 5 microns,

said resin flow rate being selected from rates in said resin flow raterange which do not exceed a maximum rate above which, for a chosencombination of gas flow rate and degraded resin apparent viscosity,coarse shot is formed, v

said maximum resin flow rate decreasing in its aforesaid range as saidgas flow rate is decreased in its range or as said degraded resin has anincreased apparent viscosity in its range, or both."

16. The method of claim 15 in which said resin is selected from C to Cpolyolefins and mixtures thereof.

17. The method of claim 16 in which said resin flow rate is at least 1.0 per minute per orifice and said apparent viscosity is from about 100to about 300 poise.

18. In a process for producing a melt-blown nonwoven mat wherein afiber-forming thermoplastic polymer resin in molten form is forced by anextruder through a row of orifices in a heated nozzle into a' stream ofhot inert gas which is issued from outlets adjacent to said row oforifices so as to attenuate said molten resin into fibers which form afiber stream, and

said fibers are collected on a receiver in the path of said fiber streamto form said non-woven mat,

the improvement of increasing the production of said non-woven matswhile preventing the inclusion of coarse shot in such mats, by themethod which comprises in combination:

subjecting a fiber-forming thermoplastic polymer resin having an initialintrinsic. viscosity of at least 1.4 to thermal degradation, at leastpartially in an extruder, for a sufficient time at a temperature withinthe range of from about 550 F. to about 900 F., effective to cause saidresin to have both a reduced intrinsic viscosity of from about 0.6 toless than 1.4 and an apparent viscosity in said nozzle orifices of fromabout 50 to about 300 poise, said heated nozzle having a temperaturewithin the range of from about 500 F. to about 900 F.,

operating said extruder so as to force said degraded resin in moltenform from said row of nozzle orifices at a resin flow rate of from about0.1 to about 5 grams per minute per nozzle orifices, and

issuing said hot, inert gas at a temperature from about 500 F. to about900 F. from said outlets at a gas flow rate of from about 2.5 to about20 pounds per minute per square inch of outlet area, effective toattenuate said extruded degraded resin into fibers having diameters offrom about 8 to about 400 microns,

said gas flow rate being selected from rates in said gas flow rate rangethat do not exceed a maximum rate above which, for a chosen combinationof resin flow rate and degraded resin apparent viscosity, coarse shot isformed,

said maximum gas flow rate decreasing. in its aforesaid range as saidresin fiow rate decreases in its range or said degraded resin has adecreased apparent viscosity in its range, or both.

19. The method of claim 18 in which said resin is selected from C to Cpolyolefins and mixtures thereof.

20. The method of claim 19 in which said resin flow rate is at least 1.0gram per minute per orifice and said apparent viscosity is from about100 to about 300 poise.

21. In a process for producing a melt-blown nonwoven mat wherein afiber-forming thermoplastic polymer resin in molten form is forced by anextruder through a row of orifices in a heated nozzle into a stream ofhot inert gas which is issued from outlets ad jacent to said row oforifices so as to attenuate said molten resin into fibers which form afiber stream, and said fibers are collected on a receiver in the path ofsaid fiber stream to form said non-woven mat,

the improvement of increasing the production of said non-woven matswhile preventing the inclusion of coarse shot in such mats, by themethod which comprises in combination.

subjecting a fiber-forming thermoplastic polymer resin having an initialintrinsic viscosity of at least 1.4 to thermal degradation, at leastpartially in an extruder, for a sufficient time at a temperature withinthe range of from about 550 F. to about 900 F., effective to cause saidresin to have both a reduced intrinsic viscosity of from about 0.6 toless than L4 and an apparent viscosity in said nozzle orifices of fromabout 50 to about 300 poise, said heated nozzle having a temperaturewithin the range of from about 500 F. to about 900 F., operating saidextruder so as to force said degraded resin in molten form from said rowof nozzle orifices at a resin flow rate of from about 0.1 to about gramsper minute per nozzle orifice, and

issuing said hot, inert gas at a temperature from about 500 F. to about900 F. from said outlets at a gas flow rate of from greater than 20 toabout 100 pounds per minute per square inch of outlet area effective toattenuate said extruded degraded resin into fibers having a diameter offrom about 0.5 to about 5 microns,

said gas flow rate being selected from rates in said gas flow rate rangewhich are not below a minimum rate below which, for a chosen combinationof resin flow rate and degraded apparent viscosity, coarse shot isformed,

said minimum gas flow rate increasing in its aforesaid range as saidresin flow rate increases in its range or said degraded resin has anincreased apparent viscosity in its range, or both. 22. The method ofclaim 21 in which said resinis selected from C to C polyolefins andmixtures thereof.

23. The method of claim 22 in which said resin flow I rate is at least1.0 gram per minute per orifice and said the improvement of increasingthe production of said non-woven mats while preventing the inclusion ofcoarse shot in such mats, by the method which comprises in combination:

subjecting a fiber-forming thermoplastic polymer resin having an initialintrinsic viscosity of at least 1.4 to thermal degradation, at leastpartially in an extruder, for a sufficient time at a temperature withinthe range of from about 550 F. to about 900 F., effective to cause saidresin to have both a reduced intrinsic viscosity of from about 0.6 toless than 1.4 and an apparent viscosity in said nozzle orifices of fromabout 50 to about 300 poise, said heated nozzle having a temperaturewithin the range of from about 500 F. to about 900 F.,

operating said extruder so as to force said degraded resin in moltenform from said row of nozzle orifices at a resin flow rate of from about0.l to about 5 grams per minute per nozzle orifices, and

issuing said hot, inert gas at a temperature from about 500 F. to about900 F. from said outlets at a gas flow rate of from about 2.5 to about20 pounds per minute per square inch of outlet area, effective toattenuate said extruded degraded resin into fibers having diameters offrom about 8 to about 400 microns,

said resin being degraded to a selected apparent viscosity in said rangeof apparent viscosities that are not below a minimum apparent viscositybelow which, for a chosen combination of resin flow rate and gas flowrate, coarse shot is formed,

said minimum apparent viscosity increasing as said gas flow rate isincreased in its range or as said resin flow rate is decreased in itsrange, or both.

25. The method of claim 24 in which said resin is selected from C to Cpolyolefins and mixtures thereof.

26. The method of claim 25 in which said resin flow rate is at least 1.0gram per minute per orifice and said apparent viscosity is from about toabout 300 poise.

27. In a process for producing a melt-blown nonwoven mat wherein afiber-forming thermoplastic polymer resin in molten form is forced by anextruder through a row of orifices in a heated nozzle into a stream ofhot inert gas which is issued from outlets adjacent to said row oforifices so as to attenuate said molten resin into fibers whichform afiber stream, and said fibers are collected on a receiver in the path ofsaid fiber stream to form said non-woven mat,

the improvement of increasing the production of said non-woven matswhile preventing the inclusion of coarse shot in such mats, by themethod which comprises in combination:

subjecting a fiber-forming thermoplastic polymer resin having an initialintrinsic viscosity of at least 1.4 to thermal degradation, at leastpartially in an extruder, for a sufficient time at a temperature withinthe range of from about 550 F. to about 900 F. effective to cause saidresin to have both a reduced intrinsic viscosity of from about 0.6 toless than 1.4 and an apparent viscosity in said nozzle orifices of fromabout 50 to about 300 poise, said heated nozzle having a temperaturewithin the range of from about 500 F. to about 900 F.,

operating said extruder so as to force said degraded resin in moltenform from said row of nozzle orifices at a resin flow rate of from about0.1 to about 5 grams per minute per nozzle orifice, and

issuing said hot, inert gas at a temperature from about 500 F. to about900 F. from said outlets at a gas flow rate of from greater than 20 toabout 100 pounds per minute per square inch of outlet area effective toattenuate said extruded degraded resin rate is at least 1.0 gram perminute per orifice and said into fibers having a diameter of from about0.5 to

about 5 microns,

said resin being degraded to a selected apparent viscosity in said rangeof apparent viscosities that does not exceed a maximum apparentviscosity above which, for a chosen combination of resin flow rate andgas flow rate, coarse shot is formed,

said maximum apparent viscosity decreasing as said gas flow rate isdecreased in its range or as said resin flow rate is increased in itsrange, or both.

28. The method of claim 27 in which said resin is selected from C to Cpolyolefins and mixtures thereof.

29. The method of claim 28 in which said resin flow apparent viscosityis from about to about 300 poise.

30. A melt-blown non-woven mat produced by the process of claim l.

31. A melt-blown non-woven mat produced by the method of claim 7. c

32. A melt-blown non-woven mat produced by the method of claim 12. l

33. A melt-blown non-woven mat produced by the method of claim 15.

34. A melt-blown non-woven mat produced by the method of claim 18.

35. A melt-blown non-woven mat produced by the method of claim 21.

36. A melt-blown non-woven mat produced by the method of claim 24.

37. A melt-blown non-woven mat produced by the method of claim 27.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,849,241 Dated Nov. 19, 1974 Robert R.-Buntin, James P. Keller, John W.Harding Inventor(s) It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

The following changes should be made to correct the spelling of the nameof one of the inventors, Robert R. Buntin:

In the masthead, "Butin et al" should read "Buntin et al".

At [75] Inventors:", "Robert R. Butin" should read "Robert R. Buntin".

Signed and Sealed this Twenty-first D a y 0 f September 1976 S E A L 1Arrest:

RUTH c. MASON Commissioner oj'Patenls and Trademarks

1. IN A PROCESS FOR PRODUCING A MELT-BORWN NON-WOVEN MAT WHEREIN AFIBER-FORMING THERMOPLASTIC POLYMER RESIN IS EXTRUDED IN MOLTEN FORMFROM ORIFICES OF A HEATED NOZZLE INTO A STREAM OF HOT INERT GAS WHICHATTENUATES SAID MOLTEN RESIN INTO FIBERS THAT FORM A FIBER STREAM, ANDSAID FIBERS ARE COLLECTED ON ARE RECEIVER IN THE PATH OF SAID FIBERSTREAM TO FORM SAID NONWOVEN MAT, THE IMPROVEMENT WHICH COMPRISESSUBJECTING A FIBER-FORMING THERMOPLASTIC POLYMER RESIN HAVING AN INITIALINTRINSIC VISOCISTY OF AT LEAST 1.4 DEGRADATION IN THE PRESENCE OF AFREE RADICALY SOURCE COMPOUND PRIOR TO EXTRUSION FORM SAID NOZZLEORIFICES UNTIL SAID RESIN HAS BOTH A REDUCED INTRINSIC VISCOSITY OF FROMABOUT 0.6 TO LESS THAN 1.4 AND AN APPARENT VISCOSITY IN SAID NOZZLEORIFICES OF FROM ABOUT 50 TO ABOUT 300 POISES.
 2. The process of claim 1wherein said resin is subjected to thermal degradation at a temperaturewithin the range from about 550* F. to about 900* F. for a period oftime effective to cause said resin to have said reduced intrinsicviscosity and said apparent viscosity.
 3. The process of claim 2 inwhich said thermoplastic polymer resin is subjected to said thermaldegradation at least partially in an extruder feeding said resin intosaid nozzle.
 4. The process of claim 3 wherein said resin is thermallydegraded in an extruder for from about 1 to about 10 minutes effectiveto cause said resin to have said reduced intrinsic viscosity and saidapparent viscosity.
 5. The process of claim 1 wherein said free radicalsource compound is selected from organic peroxides, thiyl compounds, andorgano-tin compounds.
 6. The process of claim 1 wherein saidthermoplastic polymer resin is selected from C3-C8 polyolefins andmixtures thereof which have an initial intrinsic viscosity of at least1.4.
 7. In a process for producing a melt-blown non-woven mat wherein afiber-forming thermoplastic polymer resin is extruded in molten formfrom orifices of a heated nozzle into a stream of hot inert gas whichattenuates said molten resin into fibers that form a fiber stream, andsaid fibers are collected on a receiver in the path of said fiber streamto form said non-woven mat, the improvement of producing said mat athigh resin flow rates, which comprises: extruding from said nozzleorifices, at a resin flow rate of from about at least 0.1 to about 5grams per minute per orifice, a fiber-forming thermoplastic polymerresin degraded to have both an intrinsic viscosity of from about 0.6 toless than 1.4 and an apparent viscosity in said nozzle orifices of fromabout 50 to about 300 poise.
 8. The process of claim 7 wherein saidapparent viscosity is from about 100 to about 300 poise.
 9. The processof claim 7 wherein said resin is subjected to said degradation at leastpartially in an extruder feeding said resin to said nozzle.
 10. Theprocess of claim 9 wherein said resin is subjected to a temperaturewithin the range from about 550* F. to about 900* F. for a period oftime from about 1 to about 10 minutes effective to cause saiddegradation of said resin until said resin has said apparent viscosityand said intrinsic viscosity.
 11. The process of claim 7 wherein saidresin is selected from C3-C8 polyolefins and mixtures thereof.
 12. In aprocess for producing a melt-bloWn non-woven mat wherein a fiber-formingthermoplastic polymer resin in molten form is forced by an extruderthrough a row of orifices in a heated nozzle into a stream of hot inertgas which is issued from outlets adjacent to said row of orifices so asto attenuate said molten resin into fibers which form a fiber stream,and said fibers are collected on a receiver in the path of said fiberstream to form said non-woven mat, the improvement of increasing theproduction of said non-woven mats while preventing the inclusion ofcoarse shot in such mats, by the method which comprises in combination:subjecting a fiber-forming thermoplastic polymer resin having an initialintrinsic viscosity of at least 1.4 to thermal degradation, at leastpartially in an extruder, for a sufficient time at a temperature withinthe range of from about 550* F. to about 900* F. effective to cause saidresin to have both a reduced intrinsic viscosity of from about 0.6 toless than 1.4 and an apparent viscosity in said nozzle orifices of fromabout 50 to about 300 poise, said heated nozzle having a temperaturewithin the range of from about 500* F. to about 900* F., operating saidextruder so as to force said degraded resin in molten form from said rowof nozzle orifices at a resin flow rate of from about 0.1 to about 5grams per minute per nozzle orifices, and issuing said hot, inert gas ata temperature from about 500 F. to about 900* F. from said outlets at agas flow rate of from about 2.5 to about 20 pounds per minute per squareinch of outlet area, effective to attenuate said extruded degraded resininto fibers having diameters of from about 8 to about 400 microns, saidresin flow rate being selected from rates in said resin flow rate rangewhich are not below a minimum rate below which, for a chosen combinationof gas flow rate and degraded resin apparent viscosity, coarse shot isformed, said minimum resin flow rate increasing in its aforesaid rangeas said gas flow rate is increased in its range or as said degradedresin has a decreased apparent viscosity in its range, or both.
 13. Themethod of claim 12 in which said resin is selected from C3 to C8polyolefins and mixtures thereof.
 14. The method of claim 13 in whichsaid resin flow rate is at least 1.0 gram per minute per orifice andsaid apparent viscosity is from about 100 to about 300 poise.
 15. In aprocess for producing a melt-blown non-woven mat wherein a fiber-formingthermoplastic polymer resin in molten form is forced by an extruderthrough a row of orifices in a heated nozzle into a stream of hot inertgas which is issued from outlets adjacent to said row of orifices so asto attenuate said molten resin into fibers which form a fiber stream,and said fibers are collected on a receiver in the path of said fiberstream to form said non-woven mat, the improvement of increasing theproduction of said non-woven mats while preventing the inclusion ofcoarse shot in such mats, by the method which comprises in combination:subjecting a fiber-forming thermoplastic polymer resin having an initialintrinsic viscosity of at least 1.4 to thermal degradation, at leastpartially in an extruder, for a sufficient time at a temperature withinthe range of from about 550* F. to about 900* F. effective to cause saidresin to have both a reduced intrinsic viscosity of from about 0.6 toless than 1.4 and an apparent viscosity in said nozzle orifices of fromabout 50 to about 300 poise, said heated nozzle having a temperaturewithin the range of from about 500* F. to about 900* F., operating saidextruder so as to force said degraded resin in molten form from said rowof nozzle orifices at a resin flow rate of from about 0.1 to abOut 5grams per minute per nozzle orifice, and issuing said hot, inert gas ata temperature from about 500* F. to about 900* F. from said outlets at agas flow rate of from greater than 20 to about 100 pounds per minute persquare inch of outlet area effective to attenuate said extruded degradedresin into fibers having a diameter of from about 0.5 to about 5microns, said resin flow rate being selected from rates in said resinflow rate range which do not exceed a maximum rate above which, for achosen combination of gas flow rate and degraded resin apparentviscosity, coarse shot is formed, said maximum resin flow ratedecreasing in its aforesaid range as said gas flow rate is decreased inits range or as said degraded resin has an increased apparent viscosityin its range, or both.
 16. The method of claim 15 in which said resin isselected from C3 to C8 polyolefins and mixtures thereof.
 17. The methodof claim 16 in which said resin flow rate is at least 1.0 per minute perorifice and said apparent viscosity is from about 100 to about 300poise.
 18. In a process for producing a melt-blown non-woven mat whereina fiber-forming thermoplastic polymer resin in molten form is forced byan extruder through a row of orifices in a heated nozzle into a streamof hot inert gas which is issued from outlets adjacent to said row oforifices so as to attenuate said molten resin into fibers which form afiber stream, and said fibers are collected on a receiver in the path ofsaid fiber stream to form said non-woven mat, the improvement ofincreasing the production of said non-woven mats while preventing theinclusion of coarse shot in such mats, by the method which comprises incombination: subjecting a fiber-forming thermoplastic polymer resinhaving an initial intrinsic viscosity of at least 1.4 to thermaldegradation, at least partially in an extruder, for a sufficient time ata temperature within the range of from about 550* F. to about 900* F.,effective to cause said resin to have both a reduced intrinsic viscosityof from about 0.6 to less than 1.4 and an apparent viscosity in saidnozzle orifices of from about 50 to about 300 poise, said heated nozzlehaving a temperature within the range of from about 500* F. to about900* F., operating said extruder so as to force said degraded resin inmolten form from said row of nozzle orifices at a resin flow rate offrom about 0.1 to about 5 grams per minute per nozzle orifices, andissuing said hot, inert gas at a temperature from about 500* F. to about900* F. from said outlets at a gas flow rate of from about 2.5 to about20 pounds per minute per square inch of outlet area, effective toattenuate said extruded degraded resin into fibers having diameters offrom about 8 to about 400 microns, said gas flow rate being selectedfrom rates in said gas flow rate range that do not exceed a maximum rateabove which, for a chosen combination of resin flow rate and degradedresin apparent viscosity, coarse shot is formed, said maximum gas flowrate decreasing in its aforesaid range as said resin flow rate decreasesin its range or said degraded resin has a decreased apparent viscosityin its range, or both.
 19. The method of claim 18 in which said resin isselected from C3 to C8 polyolefins and mixtures thereof.
 20. The methodof claim 19 in which said resin flow rate is at least 1.0 gram perminute per orifice and said apparent viscosity is from about 100 toabout 300 poise.
 21. In a process for producing a melt-blown non-wovenmat wherein a fiber-forming thermoplastic polymer resin in molten formis forced by an extruder through a row of orifices in a heated nozzleinto a stream of hot inert gas which is issueD from outlets adjacent tosaid row of orifices so as to attenuate said molten resin into fiberswhich form a fiber stream, and said fibers are collected on a receiverin the path of said fiber stream to form said non-woven mat, theimprovement of increasing the production of said non-woven mats whilepreventing the inclusion of coarse shot in such mats, by the methodwhich comprises in combination. subjecting a fiber-forming thermoplasticpolymer resin having an initial intrinsic viscosity of at least 1.4 tothermal degradation, at least partially in an extruder, for a sufficienttime at a temperature within the range of from about 550* F. to about900* F., effective to cause said resin to have both a reduced intrinsicviscosity of from about 0.6 to less than 1.4 and an apparent viscosityin said nozzle orifices of from about 50 to about 300 poise, said heatednozzle having a temperature within the range of from about 500* F. toabout 900* F., operating said extruder so as to force said degradedresin in molten form from said row of nozzle orifices at a resin flowrate of from about 0.1 to about 5 grams per minute per nozzle orifice,and issuing said hot, inert gas at a temperature from about 500* F. toabout 900* F. from said outlets at a gas flow rate of from greater than20 to about 100 pounds per minute per square inch of outlet areaeffective to attenuate said extruded degraded resin into fibers having adiameter of from about 0.5 to about 5 microns, said gas flow rate beingselected from rates in said gas flow rate range which are not below aminimum rate below which, for a chosen combination of resin flow rateand degraded apparent viscosity, coarse shot is formed, said minimum gasflow rate increasing in its aforesaid range as said resin flow rateincreases in its range or said degraded resin has an increased apparentviscosity in its range, or both.
 22. The method of claim 21 in whichsaid resin is selected from C3 to C8 polyolefins and mixtures thereof.23. The method of claim 22 in which said resin flow rate is at least 1.0gram per minute per orifice and said apparent viscosity is from about100 to about 300 poise.
 24. In a process for producing a melt-blownnon-woven mat wherein a fiber-forming thermoplastic polymer resin inmolten form is forced by an extruder through a row of orifices in aheated nozzle into a stream of hot inert gas which is issued fromoutlets adjacent said row of orifices so as to attenuate said moltenresin into fibers which form a fiber stream, and said fibers arecollected on a receiver in the path of said fiber stream to form saidnon-woven mat, the improvement of increasing the production of saidnon-woven mats while preventing the inclusion of coarse shot in suchmats, by the method which comprises in combination: subjecting afiber-forming thermoplastic polymer resin having an initial intrinsicviscosity of at least 1.4 to thermal degradation, at least partially inan extruder, for a sufficient time at a temperature within the range offrom about 550* F. to about 900* F., effective to cause said resin tohave both a reduced intrinsic viscosity of from about 0.6 to less than1.4 and an apparent viscosity in said nozzle orifices of from about 50to about 300 poise, said heated nozzle having a temperature within therange of from about 500* F. to about 900* F., operating said extruder soas to force said degraded resin in molten form from said row of nozzleorifices at a resin flow rate of from about 0.1 to about 5 grams perminute per nozzle orifices, and issuing said hot, inert gas at atemperature from about 500* F. to about 900* F. from said outlets at agas flow rate oF from about 2.5 to about 20 pounds per minute per squareinch of outlet area, effective to attenuate said extruded degraded resininto fibers having diameters of from about 8 to about 400 microns, saidresin being degraded to a selected apparent viscosity in said range ofapparent viscosities that are not below a minimum apparent viscositybelow which, for a chosen combination of resin flow rate and gas flowrate, coarse shot is formed, said minimum apparent viscosity increasingas said gas flow rate is increased in its range or as said resin flowrate is decreased in its range, or both.
 25. The method of claim 24 inwhich said resin is selected from C3 to C8 polyolefins and mixturesthereof.
 26. The method of claim 25 in which said resin flow rate is atleast 1.0 gram per minute per orifice and said apparent viscosity isfrom about 100 to about 300 poise.
 27. In a process for producing amelt-blown non-woven mat wherein a fiber-forming thermoplastic polymerresin in molten form is forced by an extruder through a row of orificesin a heated nozzle into a stream of hot inert gas which is issued fromoutlets adjacent to said row of orifices so as to attenuate said moltenresin into fibers which form a fiber stream, and said fibers arecollected on a receiver in the path of said fiber stream to form saidnon-woven mat, the improvement of increasing the production of saidnon-woven mats while preventing the inclusion of coarse shot in suchmats, by the method which comprises in combination: subjecting afiber-forming thermoplastic polymer resin having an initial intrinsicviscosity of at least 1.4 to thermal degradation, at least partially inan extruder, for a sufficient time at a temperature within the range offrom about 550* F. to about 900* F. effective to cause said resin tohave both a reduced intrinsic viscosity of from about 0.6 to less than1.4 and an apparent viscosity in said nozzle orifices of from about 50to about 300 poise, said heated nozzle having a temperature within therange of from about 500* F. to about 900* F., operating said extruder soas to force said degraded resin in molten form from said row of nozzleorifices at a resin flow rate of from about 0.1 to about 5 grams perminute per nozzle orifice, and issuing said hot, inert gas at atemperature from about 500* F. to about 900* F. from said outlets at agas flow rate of from greater than 20 to about 100 pounds per minute persquare inch of outlet area effective to attenuate said extruded degradedresin into fibers having a diameter of from about 0.5 to about 5microns, said resin being degraded to a selected apparent viscosity insaid range of apparent viscosities that does not exceed a maximumapparent viscosity above which, for a chosen combination of resin flowrate and gas flow rate, coarse shot is formed, said maximum apparentviscosity decreasing as said gas flow rate is decreased in its range oras said resin flow rate is increased in its range, or both.
 28. Themethod of claim 27 in which said resin is selected from C3 to C8polyolefins and mixtures thereof.
 29. The method of claim 28 in whichsaid resin flow rate is at least 1.0 gram per minute per orifice andsaid apparent viscosity is from about 100 to about 300 poise.
 30. Amelt-blown non-woven mat produced by the process of claim
 31. Amelt-blown non-woven mat produced by the method of claim
 7. 32. Amelt-blown non-woven mat produced by the method of claim
 12. 33. Amelt-blown non-woven mat produced by the method of claim
 15. 34. Amelt-blown non-woven mat produced by the method of claim
 18. 35. Amelt-blown non-woven mat produced by the method of claim
 21. 36. Amelt-blown non-woven mat produced by the method of claim
 24. 37. Amelt-blown non-woven mat produced by the method of claim 27.